The sine-bar is used for angular measurements or for location of work at given angles, as for example in measuring or checking angles with accuracy using precision gage-blocks selected for whatever dimension is required in obtaining a given angle. Precision gage-blocks are usually purchased in sets comprising a specific number of blocks of different sizes determined mathamatically so that particular heights can be obtained by combining select blocks, two or more blocks being combined by "wringing" them together with a swivelling motion causing them to adhere accurately one to another. When combining blocks for a given dimension, the object is to use as few blocks as possible, the procedure being based upon successive elimination of the right hand digit of the desired dimension. For example, the combined blocks measuring 0.1002+0.124+0.450+3.00 equals 3.6742 inches. An accurate surface plate or master flat is always used in conjunction with a sine-bar in order to form the base from which the vertical measurements are made, heretofore with precision gage-blocks in English or Metric increments of measurement. A standard length for sine-bars is five inches (also ten inches) and there are tabulated constants that represent vertical heights H for setting a five inch sine-bar (also for ten inch bars) to the required angle. Assuming that the required angle is 31.degree. 20', the sine tables show that the height H should equal 2.6001 inches. Note that the constants in the sine tables equal five times the sine of angle: thus the sine of 31.degree. 20' in the trigonometric function table is 0.52002, and 0.52002.times.5 equals 2.6001 inches. There are many such functions for the use of a sine-bar, such as finding and checking angles, measuring angles and tapers and to determine center distances etc. However, note the complexity and precision of the involved process of using combinations of gage-blocks according to the tabulated contents of the sine tables, in order to arrive at a precise angle; it being a general object of this invention to facilitate sine-bar operation with the application of direct displacement gage-blocks and supplemented by direct readings on the barrel of a micrometer that adjusts the height H with minutes of precision.
Precision gage-blocks are purchased in sets comprising a specific number of blocks of different sizes (heights). The nominal gage sizes of individual blocks in a set are determined mathamatically so that particular desired sizes (heights) can be obtained by combining selected blocks. When there is in a set no single block of exact size that is wanted, two or more blocks are combined by "wringing" them together, achieved by crosswise placement and swivaling them together with face to face pressure, causing them to adhere by virtue of their precision surface to surface engagement. It is an object of this invention to minimize the tedious reference to trig tables and the selection of blocks which requires a high degree of intelligence and considerable training, and yet always subject to inadvertance, accident, mistake and resultant discrepancies. With the present invention, no more than one or two blocks are ever employed, and fine adjustment in minutes is a direct angular reading.
Sine-bars are precision devices for measuring angles accurately and to locate work at a desired angle to some true surface, preferably a surface plate or the like. Sine-bars consist of a hardened ground and laped steel bar which has accurately spaced cylindrical plugs of equal diameter attached to or near each end. The sine-bar has notched ends receiving the cylindrical plugs which are held firmly against angular faces of the notch, for example exactly five inches or ten inches apart. The upper and lower sides of the sine-bars are parallel to the axes of the two plugs within very close limits. The exact degree of angularity which a five inch or ten inch bar makes with a plane surface is obtained by determining the precise difference in vertical height of the spaced plugs. There are various forms of sine-bars and a refinement and/or carrying forward of the sine-bar concept involves simple and compound sine plates characterized by a precision plate pivoted by a plug at one end to a base and adapted to be elevated by the plug at the other end. In compound sine plates, the work supporting sine plate employs the underlying sine plate as its base. In any event, gage-blocks have been used for elevating these sine plates respectively, and it is an object of the present invention to supplement direct displacement gage-blocks with a direct reading micrometer combined therewith for elevation of an upper part positioning plane to be disposed as to height H' from the plane of a primary sine-bar, all as hereinafter described.
Mircometers take various forms, comprised generally of two visible elements and namely a barrel and a thimble, the barrel operating on a screw having forty threads per inch so that one revolution moves the barrel and thimble one fortieth of an inch. A feature is the relationship of calibrations on one element relative to an index line on the other element. In normal practice, the barrel is provided with a straight axially disposed index line stepped off incrementally in calibrations spaced 0.025 inch, and the thimble with an edge overlying said index line and calibrated circumferentially into twenty-five equal parts. Thus, each line on the thimble represents one thousandths of an inch, while each calibration line on the barrel represents twenty-five thousandths of an inch. It is an object of this invention to provide an inside micrometer that reads in plus or minus degree of angle on the barrel as related to a sine-bar of which it is made a part, and wherein minutes of angle are available as scaled readings on the thimble. With the present invention, a vernier scale can be employed in addition to the regular scales as disclosed and claimed in my U.S. Pat. No. 4,238,888 issued Dec. 16, 1980, so that settings in degrees, minutes and seconds are made possible. In practice, sufficient accuracy is obtainable in most instances by interpolating between minute markings.